Onset Visual Evoked Potentials Research Articles

Pattern Onset ERGs and VEPs Produced by Patterns Arising From Light Increment and Decrement.

Our aim was to elaborate how on and off signals contribute to pattern ERGs and pattern visual evoked potentials (VEPs) by using pedestal patterns arising from incremental and decremental onset stimulation. Pattern onset/offset ERGs and VEPs were produced by black and white checks of 60' side length and 88% spatial contrast appearing in a 16° field for 200 ms from white (110 cd/m2), black (7 cd/m2), and gray (48 cd/m2) backgrounds and disappeared for 1000 ms. Twenty healthy subjects participated in the study (median age 19.5, range, 5-31 years), 10 of whom also underwent pattern onset/offset ERG recordings to the same stimuli (median age 25.7, range, 22-31 years). VEPs were recorded from an occipital array referred to Fz. Pattern electroretinograms (PERGs) were recorded from "Dawson-Trick-Litzkow" (DTL) plus corneal electrodes referred to ipsilateral outer canthi. There was high correlation within subjects of the VEP waveform produced by patterns arising from light increment and decrement (group mean correlation coefficient of PVEPs to check appearance from black versus white: 87%). An average of increment and decrement PERGs simulated the onset PERG from a gray background. This waveform is akin to standard International Society for Clinical Electrophysiology of Vision (ISCEV) clinical PERGs to reversing checks. In healthy individuals, the early components of the pattern onset/offset VEP waveforms are comparable to light increment and decrement pedestal stimulation. Pattern onset/offset ERGs to pedestal stimulation may be used to probe simultaneous recording of ERGs with VEPs in order to obtain an assessment of retinal ganglion cell and optic pathway function in patients with less stable fixation.

Visual but not motor processes predict simple visuomotor reaction time of badminton players

The athlete’s brain exhibits significant functional adaptations that facilitate visuomotor reaction performance. However, it is currently unclear if the same neurophysiological processes that differentiate athletes from non-athletes also determine performance within a homogeneous group of athletes. This information can provide valuable help for athletes and coaches aiming to optimize existing training regimes. Therefore, this study aimed to identify the neurophysiological correlates of visuomotor reaction performance in a group of skilled athletes. In 36 skilled badminton athletes, electroencephalography (EEG) was used to investigate pattern reversal and motion onset visual-evoked potentials (VEPs) as well as visuomotor reaction time (VMRT) during a simple reaction task. Stimulus-locked and response-locked event-related potentials (ERPs) in visual and motor regions as well as the onset of muscle activation (EMG onset) were determined. Correlation and multiple regression analyses identified the neurophysiological parameters predicting EMG onset and VMRT. For pattern reversal stimuli, the P100 latency and age best predicted EMG onset (r = 0.43; p = .003) and VMRT (r = 0.62; p = .001). In the motion onset experiment, EMG onset (r = 0.80; p < .001) and VMRT (r = 0.78; p < .001) were predicted by N2 latency and age. In both conditions, cortical potentials in motor regions were not correlated with EMG onset or VMRT. It is concluded that previously identified neurophysiological parameters differentiating athletes from non-athletes do not necessarily determine performance within a homogeneous group of athletes. Specifically, the speed of visual perception/processing predicts EMG onset and VMRT in skilled badminton players while motor-related processes, although differentiating athletes from non-athletes, are not associated simple with visuomotor reaction performance.

Motion and pattern cortical potentials in adults with high-functioning autism spectrum disorder

Autism spectrum disorder (ASD) is a condition in which visual perception to both static and moving stimuli is altered. The aim of this study was to investigate the early cortical responses of subjects with ASD to simple patterns and moving radial rings using visual evoked potentials (VEPs). Male ASD participants (n=9) and typically developing (TD) individuals (n=7) were matched for full, performance and verbal IQ (p>0.263). VEPs were recorded to the pattern reversing checks of 50' side length presented with Michelson contrasts of 98 and 10% and to the onset of motion-either expansion or contraction of low-contrast concentric rings (33.3% duty cycle at 10% contrast). There were no significant differences between groups in the VEPs elicited by pattern reversal checkerboards of high (98%) or low (10%) contrast. The ASD group had a significantly larger N160 peak (1.85 x) amplitude to motion onset VEPs elicited by the expansion of radial rings (p=0.001). No differences were evident in contraction VEP peak amplitudes nor in the latencies of the motion onset N160 peaks. There was no evidence of a response that could be associated with adaptation to the motion stimulus in the interstimulus interval following an expansion or contraction phase of the rings. These data support a difference in processing of motion onset stimuli in this adult high-functioning ASD group compared to the TD group.

Pattern and Motion-Related Visual-Evoked Potentials in Neuroborreliosis

Visual-evoked potentials (VEPs) were used for objective testing of visual functions during treatment courses of Lyme neuroborreliosis (LNB) in adult patients in the Czech Republic. In 30 LNB patients with originally delayed VEP latencies, pattern-reversal (R-VEP) and motion onset (M-VEP) VEPs were repeatedly examined within 1 to 8 years. Six patients had Lyme optic neuritis (ON), five of them displayed prolonged latencies in both R-VEPs and M-VEPs, and one had only abnormal R-VEPs. The VEP recovery to normal latency values was in three of them. In the group of 24 LNB patients without ON, 14 patients displayed prolonged latencies only to motion stimuli, and 10 patients had abnormal latencies in both R-VEPs and M-VEPs. During the follow-up period, 7 patients displayed shortening to normal latencies. In 5 patients, VEPs latencies improved only partially, and in the remaining 12 patients, VEPs did not improve at all. This study provides objective evidence that in LNB, most of the patients without clinically manifesting ON display optic pathway involvement-predominantly magnocellular system/dorsal stream function changes. In patients with ON, however, mainly the parvocellular system is affected. About half of the patients without ON improved with a relatively long-time course of latency shortening.

VEP characteristics in children with achiasmia, in comparison to albino and healthy children

Achiasmia is a rare disorder of visual pathway maldevelopment that can show diverse clinical and magnetic resonance imaging spectra. The aim of this study was to define the characteristics of visual evoked potentials (VEPs) that differentiate abnormal optic-nerve-fibre decussation in children with achiasmia versus children with albinism and healthy children. In four children with achiasmia, the following VEP characteristics were studied and compared to children with ocular albinism and with healthy control children: (a) flash and pattern onset VEP interhemispheric asymmetry; (b) flash N2, P2 and onset C1 amplitudes and latencies; (c) interocular polarity differences in interhemisphere potentials; and (d) chiasm coefficients (CCs). In the children with achiasmia, VEPs were related to an absence of or reduced optic-nerve-fibre decussation at the chiasm and showed: ipsilateral asymmetry, significantly higher VEP amplitudes over the ipsilateral hemisphere (p<0.05), interocular inverse polarity and negative CC. Other VEP features (uncrossed asymmetry and positive CC) were also seen if additional visual pathway maldevelopment (such as severe optic nerve hypoplasia and/or absence of the optic tractus on one side) were associated with achiasmia. In the children with albinism, the VEPs were related to excess optic-nerve-fibre decussation at the chiasm and showed: contralateral asymmetry, significantly higher VEP amplitudes over the contralateral hemisphere (p<0.001), interocular inverse polarity and negative CC. In achiasmia and albinism, the VEPs to flash stimulation were more robust and more clearly distinguished between the conditions compared with the VEPs to pattern onset stimulation. VEPs in achiasmia are associated with absent or reduced optic-nerve-fibre decussation, where ipsilateral interhemispheric asymmetry is associated with interocular inverse polarity and a negative CC.

VEP maturation and visual acuity in infants and preschool children

Visual processes continue to mature well into childhood, due to the development of the retina, optic nerve, visual pathway and visual cortex. Normal development of visual acuity and maturation of visual evoked potentials (VEPs) have been well studied, although rarely for their correlation. The purpose of this study was to investigate the same population of infants and preschool children for their VEP maturation to flash, pattern-reversal (reversal) and pattern-onset (onset) stimulation, which are normally used in our everyday clinical protocol, and to determine the relationships between the VEP parameters obtained and the development of visual acuity. Forty-one healthy children from 1.5 months to 7.5 years old were included. Their visual acuity for distance was tested with Teller Acuity Cards (<2 years of age) and Cambridge Visual Acuity Crowding Cards (>2 years of age). VEP latencies and amplitudes were evaluated to flash (P2 wave), reversal (P100 wave) and onset (C1 wave) binocular stimulation. For reversal and onset stimulation, checkerboard pattern (check) sizes of 25', 50' and 100' were used. Age-dependent exponential decreases in latencies to flash, reversal and onset stimulation were seen. For amplitudes, there was an age-dependent increase only to onset stimulation. There was a significant correlation between VEPs and visual acuity (P < 0.05) for latencies to flash, reversal and onset stimulation and amplitudes to onset stimulation. These findings indicate the expected maturation of flash, reversal and onset VEPs, and demonstrate their correlation to normal development of visual acuity. Maturation of VEP latencies is associated with development of visual acuity.

Detection of motion onset and offset: reaction time and visual evoked potential analysis

Manual reaction time (RT) and visual evoked potentials (VEP) were measured in motion onset and offset detection tasks. A considerable homology was observed between the temporal structure of RTs and VEP intervals, provided that the change in motion was detected as soon as the VEP signal has reached critical threshold amplitude. Both manual reactions and VEP rise in latency as the velocity of the onset or offset motion decreases and were well approximated by the same negative power function with the exponent close to -2/3. This indicates that motion processing is normalised by subtracting the initial motion vector from ongoing motion. A comparison of the motion onset VEP signals in two different conditions, in one of which the observer was instructed to abstain from the reaction and in the other to indicate as fast as possible the beginning of the motion, contained accurate information about the manual response.

Visual evoked potentials in workers with chronic solvent encephalopathy.

Two promising variations of visual evoked potentials (VEPs) were studied in solvent-exposed workers: the effect of a low-contrast stimulus in comparison with the usually applied high contrast, and the ability of pattern-onset VEP to reveal damage to specific visual cortical areas. In addition, we studied disturbances of a visual event-related potential (P300). Thirty male patients (48 +/- 9 years of age) with solvent-induced chronic encephalopathy, and 41 controls (46 +/- 8 years) without solvent exposure, participated. Pattern-reversal checkerboards with low (11%) contrast and with high (93%) contrast between the checks were used. For onset VEPs two dedicated stimulus patterns were used. P300 was elicited with an "oddball" paradigm. At low contrast the N75-P100 peak-to-peak amplitude in the controls was 9.6 +/- 4.9 microV, i.e. 57% of the amplitude at high contrast (16.3 +/- 7.2 microV). In the patients the response at low contrast was only 48% of that at high contrast; the corresponding amplitudes were 7.5 +/- 3.5 microV and 15.8+/-4.9 microV. For the pattern-onset VEPs no effect of exposure was found. With regard to the P300, the patients missed more targets (average 3.6%) than did the controls (average 0.5%). Patients had a smaller P300 amplitude (8.8 +/- 4.5 microV) than the controls (11.5 +/- 5.3 microV), and a longer latency (390 +/- 34 ms compared to 376 +/- 24 ms). The results point to a physiological basis for the solvent-induced decrease of visual contrast sensitivity as found by others by means of psychophysical methods. The results also suggest that the neurophysiological examination of the visual system in persons who have undergone exposure to toxins might be benefited by the addition of low-contrast stimuli.

Topographical Analysis of the Onset VEP in the Detection of Paracentral Visual Field Defects

Transient visual evoked potentials (VEP) were recorded simultaneously from 16 electrodes evenly placed over posterior scalp locations covering the occipital, posterior parietal and temporal areas. Interhemispheric amplitude difference of the N70 deflection was established across 6 homologous lateral electrode pairs in 15 normal controls and 32 patients with chiasmatic or retrochiasmatic cerebral lesions. Twenty-three of these had known homonymous or bitemporal field defects while 9 had normal fields on routine perimetry. Significant interhemispheric asymmetry of any single electrode pair occurred in 55% of the 32 patients with known pathology, while the cumulative yield of all electrode pairs was over 80 percent. The diagnostic yield of individual electrode pairs was significantly different: the electrode pair placed over the temporo-parietal junction detected the highest number of abnormalities. The cumulative abnormality taken over all lateral electrode pairs could be described with a curve well fitted with a probability summation function. It is inferred that the contribution of several independent generator sources is reflected in the N70 of the pattern onset VEP. The results suggest that multichannel recording of the interhemispheric amplitude distribution of the N70 of the onset VEP is useful for the evaluation of paracentral visual field defects.

Scalp VEPs and intra-cortical responses to chromatic and achromatic stimuli in primates.

We propose asimple method of monitoring separate visual pathways inlightly sedated monkeys using chromatic and achromatic gratings of low contrast, which are known to activate predominantly either parvo- or magno-systems. The scalp Visual Evoked Potentials (VEPs) are compared with simultaneously recorded intra-cortical VEPs which in turn are compared with multi-unit and single-unit responses. At isoluminance, the onset of low contrast, coarse chromatic square wave spatial profile gratings generates negative scalp VEPs which exhibit properties consistent with the activation of sustained, parvocellular-chromatic mechanisms (e.g. low-pass spatio-temporal characteristics). In monkeys, most components of chromatic onset VEPs have latencies comparable to neuronal activity within the supragranular layers of V1. Corresponding coarse achromatic gratings elicit positive VEPs which exhibit properties consistent with the activation of transient-type magnocellular mechanisms (e.g. temporal tuning to higher temporal frequencies) and which have a more complex morphology. Achromatic onset VEPs may contain early components of similar timing to activity recorded in monkey V1, but later components cannot be related to V1 generators; other sources are not known. Achromatic reversal VEPs are similar to achromatic onset, chromatic reversal and both chromatic and achromatic offset VEPs and all differ from chromatic onset VEPs. It is observed that early components of scalp-recorded chromatic-onset VEPs are related in time to some intra-cortical potentials. These VEPs are generated by low spatial frequencies and have low pass temporal characteristics. Other scalp potentials, apparently unrelated to V1 field potential activity must be generated by other sources such as extra-striate areas.

Visual evoked potentials elicited by chromatic motion onset

Visually Evoked Potentials (VEPs) were recorded in response to the onset of chromatic and luminance motion gratings of 1 cpd and luminance 40 cd m −2 subtending a 7° field. At slow speeds (≤2 cycles s −1) the motion onset response exhibits a clear amplitude minimum at isoluminance. Over the Michelson contrast range tested (0.05–0.75) the chromatic response at 2 cycles s −1 possesses a linear response function compared to the saturating function of the luminance response and the contrast dependency of the former is a factor of 5–6 times greater than for the latter. These differences are suggestive of different neural substrates for the chromatic and luminance motion VEPs at slow speeds. At 10 cycles s −1 the chromatic motion onset VEP exhibits no amplitude minimum at isoluminance and becomes more like its luminance counterpart in terms of its saturating contrast response function. Furthermore, the contrast dependency of the chromatic and luminance responses differs by only a factor of 1.6 at this faster rate. These findings are consistent with the idea of separate motion mechanisms that operate at fast and slow speeds, the latter having separate channels for colour and luminance motion.

Albinism: diagnosis by visual evoked potentials

In albinism the majority of the nerve fibers of the optic nerve originating from an eye are innervating the contralateral hemisphere. As a result of the predominantly monocular innervation of the left and right hemispheres, the unilateral activation of the visual cortex (lateralization) can be detected with visual evoked potentials (VEP). The VEPs were elicited with pattern onset stimulation. Five channels were recorded (2 channels over the left and right occipital lobe and 1 in the midline). 22 Patients with pendular nystagmus and 15 normal volunteers were examined. 5 of the normal volunteers were also examined with simulated pendular nystagmus (5-10 degrees, 1 Hz). The nystagmus was simulated by a simple galvanometer scanner based optical system. Unilateral activation of the hemispheres (lateralisation) was never detectable by normal volunteers. The lateralization of the VEP was detectable in all patients with oculocutaneous albinism with pattern onset stimulation. The pathological crossing of the nerve fibres in the optic chiasm is always detectable in oculocutaneous and ocular albinism with multichannel pattern onset VEP. The lateralization of the VEP is a more sensitive indicator of ocular albinism than other symptoms like macular hypoplasia, hypopigmentation, iris transillumination, nystagmus, reduced visual acuity et cetera.

Motion adaptation in chromatic motion-onset visual evoked potentials.

The aim of this study was to investigate the influence of motion adaptation on visual evoked potentials (VEPs) elicited by the onset of isoluminant chromatic motion. VEPs were recorded from the occipital cortex of human subjects using a sinusoidal grating stimulus of one cycle per degree which moved at either a velocity of 2 or 10 degrees/s and subtended a field of 7 degrees with a mean luminance of 30 cdm(-2). In the first experiment the effects of adaptation were investigated via the manipulation of the stimulus duty cycle which was varied between 11-90%. The results showed a significant (p < 0.001) reduction in the N2-P2 amplitude of the chromatic response. In contrast, P1-N2 amplitude was not significantly affected by motion adaptation. Subsequent experiments demonstrated that the chromatic motion onset VEP was attenuated not only following adaptation to isoluminant chromatic motion, but also to luminance motion as well. These results indicate that the chromatic motion onset VEP is just as susceptible as its luminance counterpart to motion after effects (MAEs) and as a result it is highly likely that it is a motion specific response. Furthermore, the fact that the VEP shows that there are cross-adaptation effects between motion defined by change in colour and by change in luminance, suggests that the two types of motion stimuli have inputs into a common motion mechanism.

Macular pigment and the colour-specificity of visual evoked potentials

A modified Moreland anomaloscope was used to examine two subjects, one with dense macular pigment, the other with relatively light pigmentation. Chromatic visual evoked potentials (VEPs) were elicited from these two subjects using coarse, isoluminant gratings of different sizes. Colour-specificity was verified by comparing chromatic onset VEPs (reflecting sustained activity) with chromatic reversal VEPs (reflecting mainly transient activity) and also by Fourier analysis (colour-specific responses are dominated by the fundamental, transient activity by the second harmonic). Achromatic (transient-type) intrusions, produced by large blue-green gratings could be related to the extent of subject-specific macular pigmentation.

Objective specification of tritanopic confusion lines using visual evoked potentials

The minimum distinct border (MDB) between different isoluminant hues of a bipartite field was set subjectively by adjustment and then according to a 3-point rating allowing determination of the S-cone specific (tritanopic) axis. This rating was compared with visual evoked potentials (VEPs) generated by coarse, isoluminant gratings, modulated along the same chromatic axes. Psychophysically determined tritanopic gratings elicited monophasic onset VEPs with the longest latency for each subject. Departure from this axis produced additional earlier negative components (reflecting additional response mechanisms). Colour-selective VEPs can, therefore, objectively specify tritanopic confusion lines with a comparable degree of accuracy to MDB judgements.

Amplitude and phase variations of harmonic components in human achromatic and chromatic visual evoked potentials

Occipital visual evoked potentials (VEPs) were recorded in response to low-contrast, low spatial-frequency chromatic, and achromatic gratings. Fast Fourier Transform (FFT) and time-domain analysis were used to reveal differences in harmonic content and amplitude of chromatic and achromatic response components over a wide range of temporal frequencies. The chromatic ON/OFF VEP is dominated by the fundamental component indicating that onset and offset responses are different. This type of response is typical of neurons with sustained type response characteristics. Conversely, the achromatic onset VEP contains a predominant second harmonic component in addition to the fundamental. This similarity between onset and offset responses suggests that transient mechanisms are responsible for the generation of achromatic components. Frequency analysis of VEPs elicited by phase-reversing stimuli reveals that all of the response energy is concentrated at the second harmonic of the stimulating frequency. The magnitude of the second harmonic component is maximal for achromatic stimuli and undergoes a distinct minimum for isoluminant, chromatic stimuli. This behavior indicates that under the stimulus conditions used, magnocellular neurons with transient characteristics dominate the reversal VEP.

Visual evoked potentials in children with developmental coordination disorder

SummaryChildren who demonstrate problems with skilled movement in the absence of physical handicap are formally designated as suffering from developmental coordination disorder (DCD). Diagnosis of DCD was confirmed by the ‘movement assessment battery for children’. Visually evoked potentials (VEPs) were recorded to evaluate the integrity of the visual pathway and to rule out the presence of any neurological lesions affecting visual input. Binocular, pattern onset VEPs were recorded in 14 children with DCD aged between five and seven years, and an age‐matched control group using pattern onset, high contrast, grating stimuli. Implicit times to the first and second peaks and troughs were measured, and results between the two groups were compared. Inattention and movement artefact meant that VEPs were more difficult to record within the DCD group, resulting in smaller amplitudes of the waveform, but no significant differences in the implicit times were observed between the DCD group and controls. Further research is required to determine the specific source of the neurological deficits in DCD but a problem with the integrity of the afferent visual pathway does not appear to be a causal factor.

Visual evoked potentials in children with developmental coordination disorder

Children who demonstrate problems with skilled movement in the absence of physical handicap are formally designated as suffering from developmental coordination disorder (DCD). Diagnosis of DCD was confirmed by the ‘movement assessment battery for children’. Visually evoked potentials (VEPs) were recorded to evaluate the integrity of the visual pathway and to rule out the presence of any neurological lesions affecting visual input. Binocular, pattern onset VEPs were recorded in 14 children with DCD aged between five and seven years, and an agematched control group using pattern onset, high contrast, grating stimuli. Implicit times to the first and second peaks and troughs were measured, and results between the two groups were compared. Inattention and movement artefact meant that VEPs were more difficult to record within the DCD group, resulting in smaller amplitudes of the waveform, but no significant differences in the implicit times were observed between the DCD group and controls. Further research is required to determine the specific source of the neurological deficits in DCD but a problem with the integrity of the afferent visual pathway does not appear to be a causal factor.

Topography and homogeneity of monkey VI studied through subdurally recorded pattern-evoked potentials

Using small checkerboard stimulus fields, we have recorded visually evoked potentials (VEPs) in an alert rhesus monkey from an array of 35 electrodes chronically implanted between dura and arachnoid to study mass neuronal activity in striate and peristriate visual cortex. Although the principal purpose of this work was to study in detail cortical mapping in this particular animal for future intracortical recordings, we report here the usefulness of our approach for the non-invasive study of cortical processing, in particular of cortical magnification and receptive-field properties over the central 6 degrees of the visual field. The striate and extrastriate components in the pattern onset VEP both have a double negative-going waveform, with N-P-N peak latencies of 75-100-135 ms and 90-115-160 ms, respectively, for small element sizes and moderate contrasts; latencies may be 5 ms shorter for large element sizes and high contrast. We found little activity at electrode locations over visual areas beyond V2. The waveforms and timing permit some careful speculation concerning intracortical processing and VEP generation. The complex logarithmic form of the retinotopical projection provides a satisfactory model for our data, if a value of 1-1.2 degrees is used for the offset parameter a. Our data suggest that the most abundant receptive-field size in foveal striate cortex has a center diameter of 12'. This size remains constant up to 2 degrees eccentricity, and increases only slowly up to 4 degrees. The smallest receptive-field sizes seem to be independent of eccentricity throughout the central 4 degrees of V1, with a value of 4-8', in agreement with single-cell data reported by Dow et al. (1981) and Van Essen et al. (1984).

The effect of standing contrast and pattern adaptation on the human visually evoked potential

Human visually evoked potentials (VEPs) were recorded with sinusoidal gratings of low (0.5 c/deg), medium (4 c/deg) and high (16 c/deg) spatial frequency (SF). Simultaneous recording from Oz-A1, O2-A1 and Oz-O2 allowed the separation of the early and late VEP waves for most subjects. The effect of standing contrast and pattern adaptation on these waves was studied. At low SF both early and late waves were not affected by standing contrast or adaptation with motionless grating, while adaptation with a drifting grating reduced them. At medium and high SFs both principal negative waves, N1 and N2, were reduced by standing contrast and pattern adaptation. The amplitude of N2 saturated at low contrast level (0.1) and was reduced after adaptation regardless of the SF of test and adapting stimuli, while the amplitude of N1 did not saturate up to the contrast level of 0.3 and exhibited SF-selective adaptation. The adapted onset-VEP was similar to the offset-VEP. The data suggest that: (1) the early wave is generated by multiple narrowly turned SF-selective structures that are medially positioned while the generators of the late wave are not SF-selective and occupy a wider area centered laterally; (2) the effects of standing contrast and pattern adaptation on VEPs, as well as the relationship of onset and offset VEPs, reflect the time-course of neural activity evoked by long-lasting stimuli.